Multifunctional nanomaterials can be modified with specific biomolecules to increase drug loading capacity and target specific proteins, DNA sequences, and other macromolecular structures (1-5). However, one common limitation of nanoparticle applications in clinical settings is the difficulty of tracking nanoparticle localization and movement in vivo. Significant interest has been placed on carbon-based nanomaterials such as fullerenes and nanotubes for biological applications (e.g. biosensors, drug delivery, etc.) due to their physical, chemical, and biological properties (6-14). However, the biocompatibility of these compounds remains in question (15-17).
Diamond-based nanoparticles have gained attention as an alternative carbon nanomaterial due to their excellent biocompatibility, which may be due in part to lower induction of cellular oxidative stress than is observed with other carbon nanomaterials (18-21). Although advancements are being made in covalent and noncovalent modification of the nanodiamond surface, imaging of nanodiamond particles has largely centered on optical imaging with fluorescence spectroscopy. While fluorescent nanodiamonds provide an alternative to toxic quantum dots, they suffer from limitations in tissue penetration as other optical imaging techniques, restricting their use to primarily histological applications.